Understanding and controlling morphology evolution via DIO plasticization in PffBT4T-2OD/PC71BM devices

نویسندگان

  • Yiwei Zhang
  • Andrew J. Parnell
  • Fabio Pontecchiani
  • Joshaniel F. K. Cooper
  • Richard L. Thompson
  • Richard A. L. Jones
  • Stephen M. King
  • David G. Lidzey
  • Gabriel Bernardo
چکیده

We demonstrate that the inclusion of a small amount of the co-solvent 1,8-diiodooctane in the preparation of a bulk-heterojunction photovoltaic device increases its power conversion efficiency by 20%, through a mechanism of transient plasticisation. We follow the removal of 1,8-diiodooctane directly after spin-coating using ellipsometry and ion beam analysis, while using small angle neutron scattering to characterise the morphological nanostructure evolution of the film. In PffBT4T-2OD/PC71BM devices, the power conversion efficiency increases from 7.2% to above 8.7% as a result of the coarsening of the phase domains. This coarsening process is assisted by thermal annealing and the slow evaporation of 1,8-diiodooctane, which we suggest, acts as a plasticiser to promote molecular mobility. Our results show that 1,8-diiodooctane can be completely removed from the film by a thermal annealing process at temperatures ≤100 °C and that there is an interplay between the evaporation rate of 1,8-diiodooctane and the rate of domain coarsening in the plasticized film which helps elucidate the mechanism by which additives improve device efficiency.

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عنوان ژورنال:

دوره 7  شماره 

صفحات  -

تاریخ انتشار 2017